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首页> 外文期刊>Chemistry: A European journal >Spectroscopic and Theoretical Identification of Two Thermal Isomerization Pathways for Bistable Chiral Overcrowded Alkenes
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Spectroscopic and Theoretical Identification of Two Thermal Isomerization Pathways for Bistable Chiral Overcrowded Alkenes

机译：双稳态手性过度拥挤烯烃的两种热异构途径的光谱学和理论鉴定

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摘要

Chiroptical molecular switches play an important role in responsive materials and dynamic molecular systems. Here we present the synthesis of four chiral overcrowded alkenes and the experimental and computational study of their photochemical and thermal behavior. By irradiation with UV light, metastable diastereoisomers with opposite helicity were generated through high yielding E-Z isomerizations. Kinetic studies on metastable 1-4 using CD spectroscopy and HPLC analysis revealed two pathways at higher temperatures for the thermal isomerization, namely a thermal E-Z isomerization (TEZI) and a thermal helix inversion (THI). These processes were also studied computationally whereby a new strategy was developed for calculating the TEZI barrier for second-generation overcrowded alkenes. To demonstrate that these overcrowded alkenes can be employed as bistable switches, photochromic cycling was performed, which showed that the alkenes display good selectivity and fatigue resistance over multiple irradiation cycles. In particular, switch 3 displayed the best performance in forward and backward photoswitching, while 1 excelled in thermal stability of the photogenerated metastable form. Overall, the alkenes studied showed a remarkable and unprecedented combination of switching properties including dynamic helicity, reversibility, selectivity, fatigue resistance, and thermal stability.
机译：整脊分子开关在响应材料和动态分子系统中起着重要作用。在这里，我们介绍了四种手性过度拥挤的烯烃的合成及其光化学和热行为的实验和计算研究。通过用紫外线照射，通过高产率的E-Z异构化产生具有相反螺旋度的亚稳态非对映异构体。使用CD光谱和HPLC分析对亚稳1-4的动力学研究揭示了在较高温度下热异构化的两条途径，即热E-Z异构化（TEZI）和热螺旋转化（THI）。还对这些过程进行了计算研究，从而开发了一种用于计算第二代过度拥挤烯烃的TEZI势垒的新策略。为了证明这些过度拥挤的烯烃可以用作双稳态开关，进行了光致变色循环，这表明烯烃在多个辐照循环中显示出良好的选择性和抗疲劳性。特别是，开关3在向前和向后的光开关中表现出最好的性能，而开关1在光生亚稳态形式的热稳定性方面表现出色。总体而言，所研究的烯烃显示出开关性能的显着和前所未有的组合，包括动态螺旋度，可逆性，选择性，耐疲劳性和热稳定性。

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